Process for stabilizing or deactivating sludges, precipitates, and residues occurring or used in the manufacture of tetraalkyl leads



Patented Sept. 10, 1945 'EES P'EEN'E' QFFICE PRGCESS FGR STABILIZING R DEACTIVAT- ING SLUDGES, PRECIPITATES, AND RESI- DUES OCCURBING 0B USED IN THE MAN- UFATURE 0F TETRAALKYL LEADS No Drawing. Application September 16, 1942, Serial No. 458,578

9 Claims.

This invention relates to a process for stabilizing or deactivating sludges, precipitates and residues occurring or used in the manufacture of tetraallzyl leads, and which normally tend to promote decomposition and ignition of the tetraalkyl leads that may be contained therein.

It is known that alkyl metal compounds in general are quite unstable and decompose read- 1137, particularly in the presence of air or oxygen. It has also been found that these alkyl metal compounds are particularly unstable when adsorbed on materials which present a large surface area pcr unit volume such as silica gel, clays, alumina, earths, asbestos, charcoal, and materials of similar structure which materials appear to exert a catalytic effect in the decomposition of these alkyl metal compounds. Even tetraalkyl leads such as tetraethyl lead which is known to be somewhat more stable than some of the other alkyl metal compounds decomposes and often ignites in the presence of oxygen when small amounts are adsorbed on materials that offer extended surface areas, particularly when the masses containing the tetraethyl lead are exposed to temperatures somewhat higher than normal atmospheric temperatures. The tendency to oxidize and ignite of course varies with the substance with which the alkyl metal compound is incorporated, some materials apparently exerting a greater catalytic effect than others in promoting ignition of the alkyl lead compounds.

In the manufacture of tetraalkyl leads, such as tetraethyl lead, tetramethyl lead and the mixed ethyl-methyl lead compounds, sludges are formed from which it is diflicult and, from a practical standpoint, impossible to entirely free from the alkyl lead compounds during the normal steam distillations or decantation operations. There is, therefore, carried through the process very finely divided lead and impuritie such as bismuth compounds which, although present in very small amounts, finally are deposited as sludges in the pipes and tanks and other processing equipment and these sludges which contain tetraethyl lead adsorbed therein when exposed to oxygen or air often ignite, thus presenting erious ignition and explosion hazards in the process.

Methods have been advanced for the removal of practically all the sludge forming materials from the tetraethyl lead after its distillation, such as by controlled blowing with air or oxygen with agitation, preferably under a layer of water, followed by separation of the precipitated sludge,

plication Ser. No. 393,680. However, even in these case the sludge which is deposited by the action of the oxidizing agent and which invariably contains tetraethyl lead, tend to ignite when exposed to air thus presenting serious ignition hazards, making it desirable that even these sludges should be deactivated during their formation or afterwards to permit of their removal and disposal in a safe manner.

It is therefore an object of thi invention to provide a process for stabilizing sludges, precipitates and residues occurring in the manufacture of tetraalkyl lead compounds whereby the ignition hazard presented by the lead alkyl compounds in contact with such catalytic surfaces is reduced or completely overcome.

It is a still further object of the invention to render inactive materials which tend to exert a catalytic effect in the decomposition of tetraalkyl leads in the presence of air thus permitting the safe use of such materials as filter aids in the manufacture of tetraalkyl lead.

We have found that the sludges, precipitates and residues occurring in the manufacture of tetraalkyl lead which tend to catalyze the decom-' position of tetraalkyl lead compounds contained therein when in contact with oxygen or air can be rendered relatively stable to oxidation and ig.. nition by incorporating with such materials a compound of the class consisting of alkali metal, ammonium and organic amine sulfides, polysulfides, and sulfhydrates; organic mercaptans and organic compounds which contain the sulfhydryl radical (SI-I), or compounds which contain such radical by tautomerization.

We have found that the sludges originating in the production of tetraethyl lead, or other materials such as filter aids used in the process which offer large surface area per unit volume are deactivated conveniently and economically by washing with aqueous solutions of the sulfur compounds of the types above described, irrespective of whether such materials contain the tetraalkyl lead compounds at the time they are washed with such sulfur containing solutions or whether they are later incorporated therewith. Where filter aids are employed in the filtering of the tetraalkyl lead compounds these aids such as clays, silica, earths, charcoal, etc., which tend to catalyze the decomposition of small amounts of the tetraalkyl leads contained therein may be rendered inactive by washing them with the sulfur containing compounds of the classes above mentioned so that when they are subsequently emas more particularly described in copending apployed either before or after drying in the filtration of the tetraalkyl lead they no longer cause the ignition of the residual tetraethyl lead on exposure to air even at steam bath temperatures, thus facilitating their removal from the system and final disposition.

In the storage of crude tetraalkyl lead compounds prior to final purification, sludges are formed which settle out, or in some cases collect on the surface of the alkyl lead compounds and there when exposed to air, because of the catalytic effect of the inorganic materials incorporated therein tend to ignite, offering serious fire and explosion hazards. By maintaining an aqueous solution of one of the aforementioned deactivating agents as a layer over the crude tetraalkyl lead any sludge which precipitates at the surface is deactivated on contact with the aqueous layer and the sludge is rendered inactive to air oxidation. By employing deactivating agent of the types mentioned, which are soluble in the tetraethyl lead, any sludge which precipitates while in storage is immediately rendered safe from the ignition hazard.

Where inorganic hydrogen sulfide compounds are employed they should be used in a slightly alkaline medium (in a medium of a pH greater than '7) to prevent their conversion to hydrogen sulfide which as such is ineifective in the deactivating of such sludges. These compounds are therefore preferabl employed as the alkali metal salts. The organic sulfur compounds may be used under either acidic or alkaline conditions. The water soluble mercaptans may be employed as aqueous solution while those which are water insoluble may be dissolved in suitable solvents such as benzene or alcohol and employed as such in the deactivation of the sludge or other active material in which the tetraalkyl lead compounds are adsorbed, or they may be used as suspensions in water.

Because sodium sulfide is inexpensive and readily available its use in the deactivation of sludges and residues in the manufacture of tetraalkyl leads is preferred. An aqueous solution containing an amount of sodium sulfide equivalent to approximately 33% of the dry weight of material to be stabilized has been'found to give ver satisfactory results. The amount of sodium sulfide, however, may be varied over a wide range with equally good results. For example, eificient stabilization can be effected with sodium sulfide ranging in amounts from 0.05% to 100% of the dry weight of the material to be treated. While some stabilization effect may be obtained by even smaller quantities the reduction in the ignition "a hazard with smaller quantities is not sufficient for ordinar operating conditions. The use of larger quantities in general is needless and onl adds to the cost of carrying out the process and does not materially contribute to increased safety in the disposal of the sludges and residues encountered in the manufacture and storage of the tetraalkyl lead compounds. The sodium sulfide is preferably employed in aqueous solutions of approximately 1% strength although aqueous solutions of 0.1% concentrations may be employed, the particular concentrations depending more particularly upon the volume of the apparatus in which the sludges are to be treated. Concentrations of less than 0.1% in the Wash solutions are in general not commercially practical because of the loss of the sulfide as a result of the oxidation b the oxygen dissolved from the atmosphere in the solution. In washing the adsorbed materials it is of course desirable that a sufficient quantity be employed to effect good physical contact between the solution and the adsorbed material. It has been found desirable to employ a relatively large volume of solution with a concentration of less than 5%, and onl in cases where the allowable Volume is limited is the use of concentrations above 5% necessary.

In treating the sludge, filter aid, or other active material with the sodium sulfide or other deactivating substance, the effect of the deactivat ing agent is not impaired by drying the treated material, and even with repeated washing with water, solvents, or with the tetraethyl lead the activity of the sludge or filter aid is not restored to an appreciable extent.

The following examples are given to illustrate the invention. The parts used are by weight.

EXAMPLE 1 Approximately 1000 parts of tetraethyl lead are processed in a washer to precipitate the sludge forming impurities by the method more particularly described in the co-pending application, Serial No. 393,680. The precipitated sludge, which by analysis of a small sample of crude tetraethyl lead is'calculated to weigh one part, is collected in 100 parts of water. The purified tetraethyl lead is then decanted from the water layer. Approximately 0.6 part of sodium sulfide is added to the aqueous phase producing a solution of about 0.6% sodium sulfide. The mixture is agitated for 15 minutes and filtered.

A small portion of the wet filter cake is tested for ignition activity by heating for 24 hours on the steam bath (95-l00 C.) and is found to be inactive. No signs of ignition or charring of the filter paper are noted even after 48 hours on the steam bath. At the end of the 48 hours heating, the sludge is saturated with tetraethyl lead and the test repeated. After 24 hours further heating, the test is again repeated, making a total of 72 hours testing time. No decomposition is noted at the end of these tests.

When a sample of the same sludge which is taken before the sodium sulfide is added to the Water layer is tested for activity as outlined above, ignition occurs shortly after the initial sample is placed on the steam bath.

In plant operation it may not always be convenient to run a laboratory analysis in order to determine the amount of sludge that will be present, and such a procedure is not necessary. The quantity of sludge formed per 1000 parts of tetraethyl lead seldom exceeds 2 parts and this figure may be used as a basis for the calculation of the quantity of sodium sulfide required. Therefore if 0.6 part (30% of the dry sludge weight) of sodium sulfide is added to the water layer per 1000 parts of tetraethyl lead, sufiicient deactivation is insured to meet any conditions which may be experienced. It is of course understood that tetraethyl lead manufactured in various plants may var in sludge forming material, but in any one plant the quantit is relatively constant so that a definite amount of sodium sulfide per unit weight of tetraethyl lead can be employed after determining what quantity will be adequate in all cases. As stated, the use of an amount of sodium sulfide equal to about of the expected dry weight of the sludge being deactivated is, in gen eral, satisfactory. This figure allows considerable latitude in operation, and We have found its use to be very successful in all stabilization op- ,erations.

As previously stated, we have found that other alkali sulfides, polysulfides and sulphydrates are eifective deactivators, and they may be substituted for the sodium sulfide in this example.

tetramercapto copper phthalocyanine; and alkyl mercaptans such as methyl mercaptan, amylmercaptan, octylmercaptan, and octadecylmercaptan.

The following compounds which not not contain 5 a sulfhydryl group as such, but which form this EXAMPLE 2 group by tautomerization have also been found Approximately 10,000 parts of crude tetraethyl to be effective deactivators: guanyl thiourea, lead are placed in a suitable container provided thioacetanilide, thiosemicarbazide, thiocarbazide, with means for agitating its contents. About thiobiuret, thicaceto acetic acid ester, and thio- 1,000 parts of water are added, and the sludge is 10 phenyl methyl pyrazolone. precipitated and collected in the Water layer by As in the case of the alkali metal sulfides, the the process more particularly disclosed in 00- concentration of the deactivators listed above as pending application Serial No. 393,680. examples of the types of compounds that may be After the precipitation is complete, 10 parts of employed, may be varied over wide ranges without sodium polysulfide (Nazsis) are added and the sacrificing effectiveness. In the same manner as contents of the container are agitated for about with the sulfides, quantities of these compounds 15 minutes. The tetraethyl lead and the aqueous equivalent to 0.05-l00% of the active sludge will layer are then filtered together, and the clear be found sufficient to insure good results. It is tetraethyl lead is then decanted from the water also to be noted that the quantity of stabilizing layer. A sample of the sludge retained on the agent required to deactivate the sludges originatfilter when tested for ignition activity as preing in the production of tetraalkyl lead does not viously described is found to be inactive. need to be suflicient to completely satisfy the ca- Organic compounds containing the sulfhydryl pacity of the sludge to combine with the reagent group may be applied from water as solutions if. in order to obtain satisfactor reduction of ignithey are soluble therein, or as dispersions if intion hazard, soluble, or the may be employed with suitable Wherever sludges or precipitates may settle out organic solvents. Where water is used as the in the lines, tanks and other processing equipsolvent or dispersing medium, the method of EX- merit during the manufacture of tetraethyl lead, ample 1 is effective in applying the deactivator it is desirable that these sludges and precipitates to the precipitated tetraalkyl lead sludges. Howbe periodically deactivated to insure safety in the ever, When some solvent other than water is emoperation. This is accomplished by pumpin an ployed, the aqueous layer containing the sludge aqueous solution of the deactivator, such as 1% may first be filtered, and the filter cake then agisolutions of sodium sulfide through the various tated with the solution containing the deactivatpieces of equipment in a, manner that allows a ing agent for 15 to 30 minutes, or the solvent socontact between the solution and the sludge for lution may be added directl to the aqueous from 15 to 30 minutes. sludge suspension. It is not necessary to dissolve A further use of the invention is to stabilize acthe stabilizing reagent in a solvent or the aqueous tive filter aids which are to be used in tetraalkyl phase before it is applied for we have found that lead filtration and which tend to catalyze decomdispersions or suspensions of the deactivators are positions of tetraethyl lead. These materials may equally effective. Results obtained with various be washed in a solution of sodium sulfide, or of representative materials containing a sulfhydryl one of the other deactivators and rendered inacgroup (--SH) are given in Table I below. tive as decomposition catalysts, and therefore Ten parts of active sludge are shaken with more suitable for use in tetraalkyl lead manufacparts of each of the indicated solutions. 45 ture.

Table I O0ncen Steam bath stability Compound tration. Solvent percent Initial After 24 hours After 72 hours Thioglycolic acid 5 No decomposition." No decomposition. Seleuoglycolic acid 5 C1 D0. Thio-uroa 5 D0. Thiosorbito 5 Do. Thiophenol. 5 Do. Mercapto thiazoline I. .i 5 Do. Potassium dibutyl dithio carbamate 1 Do. Ammonium sulfhydrate 2 D0. Sodium sulfhydrate g 0 Do. Calcium sulihydrate 1. Do. Potassium sulfhydrat 1. Do. Sodium selenide 1. Do. No deactivator (control) In addition to the above specific examples the following compounds which contain a sulfhydryl group have been found to be effective deactivators: thioamides such as thiocyanuric acid, dimethyl ammonium dithiocarbamate, and sodium phenyl dithiocarbamate; thio acids such as thioacetic acid, thiobenzoic acid, thiosalicylic acid and 2-merapto-3-naphthoic acid; substituted cyclic mercaptans such as thiocresol, Xylyl mercaptan, alphaand beta-thionaphthol, pinene mercaptans, terpene mercaptans, benzyl mercaptan, cyclohexylmercaptan, dithiohydroquinone, dithioresorcinol, Z-mercapto-benzothiazole and Two types of filter aids as well as a number of other materials of similar structure which offer a large surface area were saturated with tetraethyl lead and placed on a steam bath as described in Example 1 above. All were found to accelerate the ignition of the tetraethyl lead contained therein. Ten parts of each of these materials were then agitated for several hours with 50 parts of solution of sodium sulfide of the corn centrations given below in Table II. After the agitation period, the suspensions were filtered 75 and portions of the filter cakes were wet with tetraethyl lead and. placed on a steam bath. Resuits of the tests are given below:

Table II Material Wash solution Steam bath test Filter aid (clay) Ignited.

Do No decomposition. Filter aid (silica) Ignited.

Do No decomposition. Yellow lead oxide (N. F. VI) Ignited.

No decomposition. Ignited. No decomposition.

Ignited.

Do Bismuth subnitrate. Do Bismuth oxide (prepared. by

hydrolysis of Bi(NO3)3).

N decomposition. Ignited. No decomposition. Ignited. No decomposition. Ignited. No decomposition.

Do Ferric oxide (anh.)

A further important use of the invention is found in the storage of crude tetraalkyl lead fore it is desludged. An aqueous solution of one of the deactivators may be used to cover the crude tetraalkyl lead so that any sludge which separates out and collects at the surface is deactivated by contact with the aqueous layer. If desired. all of the precipitated sludge may be brought into the aqueous layer by suitable agitation since the stabilized sludge particles readily disperse in the water layer. In this way the sludge may be effectively deactivated as soon as it is formed.

The sludge formed in crude tetraethyl lead on standing may also be deactivated without the use of the aqueous layer by the use of those deacti vating agents mentioned which are soluble in tetraethyl lead so that any sludge that precipitates during storage is immediately rendered safe by the deactivator.

An aqueous solution of th deactivating agent may also be used to cover the tetraalkyl lead during the accelerated sludge precipitation treatment previously referred to and m re particularly described in co -pending application Serial No. 393,680. The stabilizing agent may conveniently be added to the water layer after the treatment is complete for, as we have already disclosed, in general, more deactivating agent is required when the agent is added before the desludging oper tion. However, adding the stabilizer before the desludging operation does offer the advantage that stabilization is effected as the sludge is formed and no additional time is required.

EXAMPLE 3 Approximately 30,060 parts of crude tetraethyl lead are placed in a suitable tank or washer, and an approximately equal weight of water is added to the tetraethyl lead. About 300 parts of thiophenol are then added to the Water layer and the sludge is precipitated and removed from the tetraethyl lead by the method disclosed in the co-pending application, Serial No. 393,680. After this operation is complete, the tetraethyl lead is removed by decantation, and the aqueous layer containing the sludge is filtered. A portion of the filter cake when saturated with tetraethyl lead and tested for ignition as described in EX- ample l is inactive.

As previously stated, sludges found in tetraethyl lead are also found in other lead alkyls which are manufactured from commercial lead. An example of these alkyls are the mixed tetramethyl-ethyl compounds of lead, formed when a mixture of methyl chloride and ethyl chloride are reacted with lead sodium alloy. All examples in which tetraethyl lead is specified are operable with these mixed. lead alkyls.

EXAMPLE 4 Approximately 8000 parts of crude mixed tetramethyl-ethyl lead compounds (tetramethyl lead, trimethyl ethyl lead, dimethyl diethyl lead. methyl triethyl lead and tetraethyl lead) are placed in a suitable tank or washer, and 2000 parts of water containing ten parts of thioglycolic acid are added. The contents of the tank are aerated and agitated for two hOllI-s as disclosed in the co-pending application, Serial No. 393,680. After a settling period of a few minutes. the clear solution of mixed lead alkyls is decanted from the aqueous layer and the aqueous mixture is filtered. A portion of the filter cake is given the steam bath stability test as described in Example 1 except that the filter cake (sludge) is wet with mixed lead. alkyl compounds rather than with tetraethyl lead. No decomposition or ignition of the lead alkyls is noted. A similar experiment carried out in which no thioglycolic acid is placed in the water layer. gives a sludge which ignites the mixed alkyls when the steam bath stability test is made.

In testing the activity of the sludges before or after treatment with the deactivating agents it will be noted that teraethyl or other alkyl lead was added to the residues. This was to make sure there wa sufficient tetraalkyl lead present to ignite under the conditions employed, if the sludge was not fully inactivated, for in some instances, it is possible that the amount of alkyllead may be reduced to such. a small amount that ignition might not be noted. While the elimination of the alkyl lead from the residues to such an extent does not ordinarily take place, the tests were made under conditions favoring ignition provided the sludge or filter aid was active.

The sulfur compounds employed in the deactivation of the sludges, do not destroy or alter the properties of the alkyl lead itself, nor do they appear to decrease the property of the sludge to adsorb the alkyl lead. It is therefore difiicult to explain the theory of how these catalytic materials are rendered inactive.

This invention makes possible the deactivation of the ignitable sludges and residues occurring in the manufacture of tetraalkyl lead compounds and is of particular value in eliminating fire and explosion hazards involved in the removal and disposal of such sludges from the process and in overcoming the potential fire hazard arising from the collection of such sludges and precipitates which accumulate in various places in the processing equipment an which when exposed to air often ignite with considerable damage. The invention also permits the use of filter aids which unless rendered inactive tend to cause ignition of any absorbed tetraethyl lead when they are exposed to the air. Any other absorbent materials which for any reason may become saturated with tetraethyl lead in or about the plant in which it is being manufactured may be rendered inactive by washing or otherwise treating with stabilizers of the type described so that potential fire hazards may be removed as far as possible. Lagging on pipe which due to leaks may become saturated, with tetraethyl lead and which have been known to cause its ignition can be inactivated by treating such lagging with the deactivating agents.

We claim:

1. The process of inhibiting spontaneous ignition of tetraalkyl lead compounds adsorbed on sludges which are precipitated from crude steam distilled tetraalkyl lead compounds and which sludges normally tend to cause spontaneous ignition of the tetraalkyl lead compounds adsorbed thereon upon exposure to oxygen, which comprises incorporating with such sludges an aqueous solution of a compound of the class consisting of alkali metal and ammonium monosulfides, polysulfides and sulfhydrates.

2. The process of inhibiting spontaneous ignition of tetraethyl lead adsorbed on sludges Which are precipitated from crude steam distilled tetraethyl lead and which sludges normally tend to cause spontaneous ignition of the tetraethyl lead adsorbed thereon upon exposure to oxygen, which comprises incorporating with such sludges an aqueous solution of a compound of the class consisting of alkali metal and ammonium monosulfides, polysulfides and sulihydrates.

3. The process of inhibiting spontaneous ignition of tetraethyl lead adsorbed on sludges which are precipitated from crude steam distilled tetraethyl lead and which sludges normally tend to cause spontaneous ignition of the tetraethyl lead adsorbed thereon upon exposure to oxygen, which comprises washing suchsludges with an aqueous solution of a compound of the class consisting of alkali metal and ammonium monosulfides, poly sulfides and sulihydrates.

4. The process of inhibiting spontaneous ignition of tetraethyl lead adsorbed on sludges which are precipitated from crude steam distilled tetraethyl lead and which sludges normally tend to cause spontaneous ignition of the tetraethyl lead adsorbed thereon upon exposure to oxygen, which comprises washing such sludges with an aqueous solution of an alkali metal sulfide.

5. The process of inhibiting spontaneous ignition of tetraethyl lead adsorbed on sludges which are precipitated from crude steam distilled tetraethyl lead and which sludges normally tend to cause spontaneous ignition oi the tetraethyl lead adsorbed thereon upon exposure to oxygen, which comprises washing such sludges with an aqueous solution of sodium sulfide.

6. The process for separating and deactivating sludges from crude steam distilled tetraethyl lead and which sludges normally tend to cause spontaneous ignition of tetraethyl lead adsorbed thereon upon exposure to oxygen, which comprises placing a layer or an aqueous solution of a compound of the class consisting of alkali metal and ammonium monosulfides, polysulfides and suit-hydrates on the surface of a body of crude steam distilled tetraethyl lead containing sludgeforming materials, causing the formation and separation of the sludge from the tetraethyl lead to the aqueous layer, and removing the sludgecarrying aqueous layer from the tetraethyl lead.

7. The process for separating and deactivating sludges from crude steam distilled tetraethyl lead and which sludges normally tend to cause spontaneous ignition of tetraethyl lead adsorbed thereon upon exposure to oxygen, which comprises placing a layer or" an aqueous solution of an alkali metal sulfide on the surface of a body of crude steam distilled tetraethyl lead containing sludge-forming materials, causing the formation and separation of the sludge from the tetraethyl lead to the aqueous layer, and removing the sludge-carrying aqueous layer from the tetraethyl lead.

8. The process for separating and deactivating sludges from crude steam distilled tetraethyl lead and which sludges normally tend to cause spontaneous ignition of tetraethyl lead adsorbed thereon upon exposure to oxygen, which comprises placing a layer or" an aqueous solution of sodium sulfide on the surface of a body of crude steam distilled tetraethyl lead containing sludgeforming materials, causing the formation and separation of the sludge from the tetraethyl lead to the aqueous layer, and removing the sludgecarrying aqueous layer from the tetraethyl lead.

9. The process for separating and deactivating sludges from crude steam distilled tetraethyl lead and which sludges normally tend to cause spontaneous ignition of tetraethyl lead adsorbed thereon upon exposure to oxygen, which comprises placing a layer of an aqueous solution of a compound of the class consisting of alkali metal and ammonium monosulfides, polysulfides and sulfhydrates on the surface of a body of crude steam distilled tetraethyl lead containing sludgeiorming materials, storing the tetraethyl lead with the layer of aqueous solution during the formation and separation of the sludge from the tetraethyl lead to the aqueous layer, and removing the sludge-carrying aqueous layer from the tetraethyl lead.

FREDERICK B. DOWNING. ADRIAN L. LINCH. 

